The present invention relates to power returnable coilable rules of the type employing spools within which are wound the power return spring and coilable blade.
Power returnable coilable rules have proven highly advantageous and are presently widely employed. Because the measuring blades occasionally require replacement, such rule assemblies desirably permit the substitution of replacement cartridges.
Replacement cartridges heretofore have been widely utilized and are exemplified by those shown in Brown et al U.S. Pat. No. 3,689,004 granted Sept. 5, 1972; West U.S. Pat. No. 3,716,201 granted Feb. 13, 1973; and Rutty et al U.S. Pat. No. 4,067,513 granted Jan. 10, 1978. Although such replacement cartridges have been advantageously employed, some have required loose hubs, separate posts, relatively large diameter hubs or relatively expensive case or spool design.
It is an object of the present invention to provide a novel power returnable coilable rule utilizing a replaceable cartridge with a trapped internal hub engaged with the casing.
It is also an object to provide such a coilable rule in which the hub of the spool cartridge is of relatively small diameter to enhance the effectiveness of the return spring motor.
Another object is to provide a novel cartridge for a power returnable coilable rule employing a spool with a self-contained hub readily engageable by the casing in which it is to be mounted.
Still another object is to provide such a cartridge and a retaining clip assembly which securely retains the coiled spring and blade in the predetermined coiled condition and which may be readily disassembled.